kernel: optimize LcmInt for small inputs

This gives a tiny speed boost, but more importantly, avoids
unnecessary allocation of temporary memory

Before:

gap> for i in [1..10000000] do LcmInt(2^50*13, 2^50*17); od; time;
2655
gap> for i in [1..10000000] do LcmInt(2^60*13, 2^60*17); od; time;
4450
gap> for i in [1..10000000] do LcmInt(2^70*13, 2^70*17); od; time;
5831

After:

gap> for i in [1..10000000] do LcmInt(2^50*13, 2^50*17); od; time;
2381
gap> for i in [1..10000000] do LcmInt(2^60*13, 2^60*17); od; time;
4505
gap> for i in [1..10000000] do LcmInt(2^70*13, 2^70*17); od; time;
5854

src/integer.c

@@ -2199,6 +2199,15 @@ Obj LcmInt(Obj opL, Obj opR)
  if (opL == INTOBJ_INT(0) || opR == INTOBJ_INT(0))
  return INTOBJ_INT(0);
 
+ if (IS_INTOBJ(opL) || IS_INTOBJ(opR)) {
+ if (!IS_INTOBJ(opR)) {
+ SWAP(Obj, opL, opR);
+ }
+ Obj gcd = GcdInt(opL, opR);
+ opR = QuoInt(opR, gcd);
+ return AbsInt(ProdInt(opL, opR));
+ }
+
  sizeL = SIZE_INT_OR_INTOBJ(opL);
  sizeR = SIZE_INT_OR_INTOBJ(opR);